This invention relates to an access control method for a shared I/O device.
As a method for operating a first guest OS and a second guest OS on a hypervisor, and keeping the first guest OS operating even after a failure occurs to the hypervisor, a method described in Japanese Patent Application Laid-open No. Hei 5-12045 is known.
The method involves (1) exclusively assigning a physical address area to the first guest OS so that a physical address (guest absolute address) used by the first guest OS operating on the hypervisor and a host absolute address are the same, (2) exclusively assigning the first guest OS with a physical CPU having the same CPU number as a CPU number used when the first guest OS operates on the hypervisor, and (3) exclusively assigning the first guest OS with a physical interrupt having the same interrupt number as an interrupt used when the first guest OS operates on the hypervisor. Then, when the hypervisor fails, subsequently, the first guest OS continues execution not on the hypervisor but on physical hardware. The physical address, the CPU number, and the interrupt number are the same both on the hypervisor and the physical hardware, and hence the first guest OS can continue operation even after the hypervisor fails.